1. Field of the Invention
The present invention relates to a starter for an engine equipped with a motor generator employed for a hybrid vehicle provided with a power generating function and, more particularly, to a starter for an engine equipped with a motor generator that has achieved lower cost by reducing the load on the motor generator at the time of startup at low temperature, for which the engine requires a higher assist torque, so as to reduce the sizes and capacities of circuit elements.
2. Description of the Related Art
Hybrid vehicles equipped with motor generators have conventionally been well known. In this type of vehicles, the motor generator interlocked with the engine is used to convert engine output to generated electric power and to assist the engine output as necessary.
Normally, when the vehicle is traveling, the battery is charged by the rotary output of the engine; at the time of torque assist when the engine is started up, a startup torque is supplied to the engine by the battery output. This makes it possible to obviate the need of a startup motor that responds to a key switch.
FIG. 3 is a block diagram schematically showing the starter for an engine equipped with a motor generator employed for a conventional hybrid vehicle.
In FIG. 3, a motor generator 2 employing an induction generator is directly connected to an engine 1.
Connected to the motor generator 2 is an inverter 3 serving as the power supply of the motor generator 2.
Connected to the inverter 3 is a battery 4 and a motor generator control circuit 5.
The inverter 3 has an AC terminal, a DC terminal, and a control terminal. The motor generator 2 is connected to the AC terminal; a battery 4 is connected to the DC terminal; and a motor generator control circuit 5 is connected to the control terminal.
The motor generator control circuit 5, for example, receives start signal Qe from a key switch 6, and the operational information from various other types of sensors. The motor generator control circuit 5 controls the inverter 3 in accordance with the operating condition of the engine 1.
More specifically, to make the motor generator 2 function as a driving motor for startup or the like, for example, the motor generator control circuit 5 converts the electric power of the battery 4 from direct current to alternating current by the inverter 3 to control the drive of the motor generator 2.
To make the motor generator 2 function as a generator, the motor generator control circuit 5 converts the generated power of the motor generator 2 by the revolution of the engine 1 from direct current to alternating current by the inverter 3 to charge the battery 4.
Thus, the motor generator 2 works as a driving motor at the time of assisting torque for starting the engine 1, while it works as a generator at the time of power regeneration during travel or at the time of braking.
As described above, the starter for the engine equipped with the motor generator is capable of providing the torque assisting function for the engine 1 and the power generating function by employing the motor generator 2.
Furthermore, when the engine 1 is in a warm-up state, the required torque for startup is small; hence, the motor generator 2 can be made smaller and the capacities of the power element in the inverter 3 and the battery 4 can be reduced.
When, however, starting up the engine 1 at a low temperature, i.e. when the engine 1 has not yet been fully warmed up, the engine 1 requires a larger torque; therefore, in order to make up for the torque of the engine 1 supplied using only the motor generator 2, it is necessary to make the motor generator 2 larger and also to increase the capacities of the power element in the expensive inverter 3 and the battery 4.
Thus, the conventional starter for the engine equipped with the motor generator employs only the motor generator 2 to assist the output torque of the engine 1; hence it has been presenting a problem in that achieving a satisfactory assisting function requires the motor generator 2 be made larger and the capacities of the inverter 3 and battery 4 be increased, leading to higher cost.